Fischer-Tropsch catalysts partially or wholly deactivate due to a variety of factors, including poisoning by nitrogen-containing or sulfur-containing compounds and physical degradation, or attrition, of the solid catalyst particles. The catalyst activity decline translates into a loss of hydrocarbon production. There are strong economic incentives to maintain catalyst activity and hydrocarbon production without introducing additional catalyst to the system. With decreasing activity, Fischer-Tropsch catalysts often also display increasing selectivity for lighter, i.e., C4-, hydrocarbons.
Several methods of regenerating Fischer-Tropsch catalysts which have been deactivated are known. For example, a slurry Fischer-Tropsch catalyst may be regenerated by contacting the slurry with hydrogen or a hydrogen-containing gas. Yet other known processes contact the used catalyst with an oxygen containing gas or steam. Such processes may be used to remove carbon material from the catalyst surface or to alter the oxidation state of the active metal in the catalyst. In such processes, the catalyst must generally then be reactivated by a reduction step with a hydrogen-containing gas. In yet another known regeneration process, the spent catalyst is dissolved, the active metal is re-precipitated and recovered, and the catalyst re-manufactured using the recovered metal.
Catalyst activity is also lost by physical degradation. In all fluidized processes, catalyst particles suffer attrition to a certain extent. The degree of physical attrition is determined by the turbulence of the system and the strength of the catalyst particles. The degree of attrition may depend also on the process conditions in the Fischer-Tropsch reactor, such as the water partial pressure. The fines material product of attrition tends to accumulate in the Fischer-Tropsch Reactor (FTR) with a detrimental impact on the solid/liquid separation steps. The fines population is controlled by a fines removal process or frequent purging of the FTR, resulting in the loss of significant amounts of Fischer-Tropsch catalyst.
In virtually all known regeneration processes, the slurry taken from a specific Fischer-Tropsch reactor is returned to the same reactor after regeneration. Thus, the Fischer-Tropsch catalyst is subjected to the same conditions which led to deactivation.
There remains a need, therefore, for an improved and a more cost effective method to manage the Fischer-Tropsch catalyst and to increase the impact of catalyst regeneration.